I did YouGov surveys because it gave an opinion to the media (Times, etc use them) on political stances, and paid per survey.
My only gripe with them is that given the rate they send surveys and the £50 trigger before they'll pay up, it took me nearly 3 years just to get one cheque. Sure it wasn't a heck of a lot of work, but I can't be bothered with something that slow so after the cheque I stopped replying.